Initial bringup -- Exception vector

I am trying to debug why why I never gets to the kernel vectors.
I have noticed that VBAR address is reset to 0×0 every now and then, I have tried to set it , and traced things done to the first SWI called (OS_Heap in ArthurSwis).

Before I raise a ticket, where is the vector located, is it at ZeroPage &ffff0000 or is it some offset from that?

I am pretty sure that I have been able to set VBAR before in my tests but I will go back to it if I can’t get it to work in kernel.

Setting vbar doesn’t have any effect , but I have made a workaround that seems to work. I trap the SWI and constructs the pc adjustment myself.

Thanks for reading my “rants” !

RISC OS 511MB

Supervisor

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Haha , but my input thing isn’t working properly .. considering moving out keyboard reading to host before having proper
drivers.

RISC OS 511MB

Supervisor

modules
*modules

N%.%P%s%t%o% o%k%p%c %a%e
1 FC0485E4 00000000 U
2 FC078014 20000014 T
3 FC08BC7C 200000F4 M
4 FC08D068 20001A14 U
5 FC08EC24 00000000 B
6 FC0A0038 20001B74 I

Hmm MessageTrans not working?

What are we looking at here?

What are we looking at here?

RISC OS running on the Unicorn cpu emulation. No other hardware emulation.
It is a bit tricky to get it to work.. plan is to move it to Genode when
lowlevel stuff works as they should. Right now I can’t switch to USR mode,
ending up in a crash as soon as I try to do a SWI after. Might be a rights
issue.

I only have drivers to communicate with RISC OS, right now only my little UART hack.

A fun adventure will be hardware interrupts. I can probably map up host GIC and get info
from it. But when a interrupt happens it will get to running core , and taking it to
RISC OS isn’t simple. But I think I will figure something out.

No. Position Workspace Name
1 FC0485E4 00000000 UtilityModule
2 FC078014 20000014 TerritoryManager
3 FC08BC7C 200000F4 MessageTrans
4 FC08D068 20001A14 UK
5 FC08EC24 00000000 BASIC
6 FC0A1070 20001B74 International

Much better.. managed to get vectors to be honored in emulation (HACK !)
User mode works in basic , but not in ModHand.. Basic exists when started , like this:

ARM BBC BASIC V © Acorn 1989

Starting with 263139580 bytes free.

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Basic works , turned out that I needed to run it with “Own errors” disabled.

>RUN
1
2
3
4
5
6
7
8
9
10
>*modules
No. Position Workspace Name
1 FC0485E4 00000000 UtilityModule
2 FC078054 20000014 PCI
3 FC07A0D4 200001F4 FileSwitch
4 FC086FB8 200016B4 ResourceFS
5 FC087CB8 200016F4 TerritoryManager
6 FC08A0D0 00000000 Messages
7 FC09DFCC 200017F4 MessageTrans
8 FC09F3B8 00000000 SharedCLibrary
9 FC0D48A4 20003334 Debugger
10 FC0E6B68 20003634 UK
11 FC0E8724 00000000 BASIC
12 FC0F9BE4 20003794 International
13 FC0FFECC 00000000 Obey
>

More exception fun: I have managed to inject a simulated hardware interrupt. In this little experiment I simulate the timer 0 interrupt. It works , the centiclock ticks just fine , when I trigger it with a keypress.

However after time ticking I get this error:

Error: Address exception at &90000113 (Error Number &80000003)

Maybe someone can tell me what might cause this?

Where is it picking up a non word aligned address from? Some sort of calculated offset gone awry?

&90000113

That looks suspiciously like a PSR, so possibly stack related…one too many or too few registers being pulled from the stack somewhere?

That looks suspiciously like a PSR, so possibly stack related…

+1

&90000113 = N, V, Abort mask, SVC32

Thanks for your suggestion..
It turned out cpu never got into exception state. After a lot of thinking and hacking I got it to work. The timer interrupt is now triggered by a timer.

RISC OS 511MB

Cortex-A15 Processor

No keyboard present – autobooting
Supervisor

*time

Fri,02 Jan 1970.00:00:03
*time

Fri,02 Jan 1970.00:00:09
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